Tooth bleaching or "whitening" was in the past limited to the treatment of teeth discoloration which was primarily an affliction of middle-aged and older dental patients where teeth discoloration was prevalent. Discolored teeth results generally from intrinsic or extrinsic stains. Intrinsic stains are attributable to highly mineralized water, particularly water containing a high concentration of iron or fluoride which cause teeth to discolor upon being absorbed into the body or from tetracycline stains, which occur, in utero during the third trimester of pregnancy. Extrinsic stains are diet related and result primarily from smoking or drinking coffee and/or tea.
The bleaching of teeth has now become an accepted cosmetic practice of young patients as well as older patients who desire to give themselves a more youthful appearance by whitening their teeth. The traditional bleaching procedure of using a strong concentrate of hydrogen peroxide, typically a bleaching solution of 35% hydrogen peroxide, is still in current practice in the dental office either by the dentist or dental practitioner using a rubber dam to protect the gingiva. During this process the hydrogen peroxide may be heated externally to raise the temperature of the reaction and speed up the bleaching process. The external application of heat activates the dissociation of the peroxide.
It is however now more commonplace to carry out the bleaching process using a peroxide gel as the bleaching agent both in the dental office and particularly where the bleaching process is intended to be self applied by the patient in the home. The peroxide gel generally consists of a carbamide or a hydrogen peroxide composite composition. When bleaching is carried out in the dental office a source of heat may also be applied from a dental curing light or other light source such as a laser. The rubber dam is still used to protect the gingiva when the bleaching operation is carried out in the dental office. For home use bleaching applications a custom made bite tray is used to accommodate self treatment by the patient. For home application the bleaching agent consists of a lower concentrate peroxide such as 10% carbamide peroxide.
The drawbacks of present day bleaching systems both for home use and in the dental office are numerous. For example, the requirement of using an external heat source as a means of activation usually requires both the dentist and a dental assistant to spend a considerable amount of time with the patient while the bleaching process takes place. This is not an economical use of the dentists' time. As such, home bleaching has assumed a greater role where the dentist provides instruction and supervision only. Even when the bleaching operation is practiced in the dental office, reliance upon a 35% liquid hydrogen peroxide concentrate is dangerous despite the use of a rubber dam since it can spill or splash and the droplets that are dispensed are imprecise. Alternatively, mixing a powder and a liquid is inaccurate, time consuming and messy. Even systems that contemplate the use a bleaching gel instead of a liquid depend upon the normal breakdown of hydrogen peroxide which is a relatively slow operation and accordingly require additional energy from an external heat source such as a dental curing light or a laser.
A preferred dental bleaching system for use by a dental practitioner in the dental office or for self application by a patient at home should require little, if any, individual attention, operate over a controlled relatively short time period and most importantly, particularly for home use, provide an automatic indication of when the bleaching treatment can be terminated i.e., when the bite tray may be removed for replacement at a later time with a fresh bleaching composition. A bleaching system which provides some of the above features is taught in U.S. Pat. No. 5,032,178. However, the bleaching composition taught in this patent is intended to be activated using an externally applied heating source such as a dental light to avoid a bleaching time period which is extraordinarily long. In addition, although the redox color indicator guinea green is identified in the above patent to react during the bleaching operation so as to provide the patient with an indication of the termination of the bleaching operation, in fact, it neutralizes to become colorless which, as a practical matter, is not readily discernable or distinguishable from the color of tooth enamel. More specifically guinea green turns the bleach composition from green to white which does not contrast well against the white color of tooth enamel. Furthermore, the bleaching composition is intended to be hand mixed from a powder and liquid H.sub.2 O.sub.2 formulation prior to use which is inaccurate and not particularly safe or convenient particularly for home use.